This is the 2123rd most frequent Arabic word.
صعب
Difficult.
The word 'صعبة' describes the difficulty level of the problem in this sentence, functioning as an adjective.
المسألة كانت صعبة للغاية.
The problem was very difficult.
The adjective 'صعبة' here describes the subject mathematics, expressing a personal opinion about its difficulty.
أجد الرياضيات مادة صعبة.
I find mathematics a difficult subject.
The word 'صعوبة' (difficulty) in this sentence is a noun derived from 'صعب', used to indicate the challenging nature of the road.